Henry B. Hyde founded the Equitable Life Assurance Society of New York City in 1859. Along with the company papers, the collection contains family materials, including a number of letters from Hyde's sister, wife, and stepmother.

Letters from Lucy B. B. Hyde (Henry B. Hyde's sister) written to her father, Henry H. Hyde, in 1869 while she was living in New York City and studying drawing, reveal her independent nature, her dislike of materialism, and her ideas about spirituality. Lucy had traveled to Europe and in her letters tried to convince her father to travel abroad with her.

Letters from Annie Hyde to her husband, Henry B. Hyde, written while he was traveling around the world, describe her daily occupations, including visiting friends, museums, the theater, and church. She considered traveling to England to meet her husband but decided she did not want to leave her children, but also stated that she was "too timid, too much of a baby" to make the trip across the Atlantic alone.